The present invention relates to a highly hygroscopic polyamide fiber suitable for use as a raw material in comfortable garments including innerwear and leg wear.
Polyamide fiber, one of synthetic fibers, is characterized by high strength, good wear resistance, soft hand, luster, and dyeability in bright colors. Therefore, it has found use particularly for garments such as panty hose (leg wear), innerwear, and sports wear. Typical examples of innerwear include lingerie and foundation garments which are characterized by drapability, smooth surface touch, and cool feeling which are characteristic of polyamide fiber. Panty hose of polyamide fiber is favored for its high strength, good wear properties, and soft hand.
By contrast, natural fiber represented by cotton and wool is characterized by its good hand and clothing comfort. Cotton is most commonly used for innerwear and underwear (in direct contact with the skin) because of its adequate moisture absorptivity. Unfortunately, cotton innerwear lacks drapability and luster and hence looks poor. In addition, it is not comparable to polyamide innerwear in surface smooth touch and cool feeling. Therefore, cotton is not suitable especially for women's innerwear.
On the other hand, thermoplastic synthetic fiber such as polyamide fiber and polyester fiber is inferior in moisture absorptivity to natural fiber despite its high strength and good color fastness. Therefore, it does not completely absorb moisture due to perspiration inside the garment. Moisture remaining unabsorbed inside the garment causes discomfort at high temperature and high humidity in summer. When it comes to clothing comfort, polyamide fiber is not yet satisfactory although it is higher than polyester fiber in equilibrium moisture regain (moisture absorptivity in the standard state).
The present inventors previously proposed a new technology of improving the moisture absorptivity of polyamide fiber by incorporating polyamide with polyvinylpyrrolidone (PVP for short hereinafter) and polyether amide (PEA for short hereinafter). (Japanese Patent Laid-open No. 150414/1995) The resulting polyamide fiber has improved moisture absorptivity as intended but is poor in color (and hence is not suitable for garments which need a good appearance). In addition, it is liable to frequent breakage during spinning in the case of extremely fine filaments or odd-shaped filaments designed for good hand.
The present inventors also proposed a new technology for producing hygroscopic polyamide fiber with good whiteness by incorporating polyamide with PVP and a reducing agent. (Japanese Patent Laid-open No. 150415/1995) This technology yields fiber which looks almost white but still has a yellowish color attributable to PVP and hence is unsatisfactory in yellowness unless dyed. In addition, this fiber is liable to frequent breakage during spinning in the case of extremely fine filaments or odd-shaped filaments.